1. Field of the Invention
The present invention relates to a fireproof cover for a tubular lock.
2. Description of the Related Art
FIGS. 1 and 2 of the drawings illustrate a conventional tubular lock comprising an inside assembly 1, an outside assembly 2, and a latch mechanism 3. The inside assembly 1 includes an inside handle 11, an inside rose 12, an inside rose liner 13 mounted inside the inside rose 12, and an inside spindle 16 extending through the inside rose 12 and the inside rose liner 13. The outside assembly 2 includes an outside handle 21, an outside rose 22, an outside rose liner 23 mounted inside the outside rose 22, and an outside spindle 26 extending through the outside rose 22 and the outside rose liner 23. A housing 24 is formed on an inner face of the outside rose liner 23, and a locking/unlocking bar 25 is mounted to an end of the outside spindle 26.
The latch mechanism 3 is mounted between the inside rose liner 13 and the outside rose liner 23 and includes a casing 30, a latch 31, and a cam 32 that has a through-hole 321 through which the locking/unlocking bar 25 extends. When either handle 11, 21 is turned, the locking/unlocking bar 25 is turned to retract the latch 31 inward, achieving the unlatching operation.
The housing 24 includes two diametrically disposed mounting portions 241 each having a screw hole 242, and the inside rose liner 13 includes two holes 130 aligned with the screw holes 242, with two screws 14 respectively extending through the holes 130 of the inside rose liner 13 into the screw holes 242 of the housing 24. The inside rose liner 13 and the outside rose liner 23 are thus engaged, and the main portion of the lock is fixed in a borehole 81 of a door 8.
To assure sufficient strength for the lock and to cut the manufacturing cost, most parts of the conventional tubular lock are made of zinc alloy. Although zinc is cheaper than steel and possesses certain strength, the zinc alloy has a low melting point. Thus, when the tubular lock is mounted to a fireproof door, the outside rose liner 23 and the housing 24 melt when subjected to fire, as the mounting portion 241 inside the outside rose liner 23 is formed on the housing 24 that has a relatively low strength. As a result, as illustrated in FIG. 3, the inside rose liner 13 and the outside rose liner 23 are disengaged from the door and fall, exposing the borehole 81 in the door 8. The fireproof door malfunctions, as smoke and fire could not be barred.